However, since i saw in the guide that relational active record also supports joins, i still really would like to know whether it is possible to do this query from my first post in this thread using plain relational active record instead of having to use findAllBySql.

Yes, you can do this using relational AR.
There is a unit test for this scenario in the Yii SVN.
Please refer to /tests/ut/framework/db/ar/CActiveRecordTest.php and /tests/ut/framework/db/data/models.php about class "Category".